You can’t go by the validity period shown in a nonimmigrant visa, since it relates only to the period during which it may be used in making application for admission into the United States. The US Immigration authorities at the port of entry determine how long you can stay on a nonimmigrant visa. You can be deported if you stay longer.
You become a permanent resident after qualifying and being registered by the Immigration Service. This status allows you to live permanently in the US, to travel in and out without a visa, to work at any job and to accumulate time toward US citizenship. Now you’ve gotten your green card.
Can you be a dual citizen of the United States of America and another country? Yes you can — if you have been a dual citizen from birth or childhood, or you became a citizen of another country after already having US citizenship, you may qualify for dual citizenship. As long as the other country in question does not have any laws or regulations requiring you to formally renounce your US citizenship before US consular officials, then current US law unambiguously assures your right to keep both citizenships for life.